You could say either, but both have different meanings.
"the traffic here is very convenient" may imply different meanings based on context. Such as there is very little traffic in your way making transportation fast.
"the transport here is quite convenient" however could imply that there is transport easily accessible, but does not explicitly state there is little traffic, or imply that transportation is fast/reliable, only the fact that it is easily accessible.
Most people would just say the transportation is convenient, but add further context to the situation.
Not a teacher.....Yet
Student or Learner